Page 260 - Anatomy and Physiology of Farm Animals, 8th Edition

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Animals with injury to one side of open into a shallow furrow near the
mucocutaneous junction of the eyelid. The
VetBooks.ir their vestibular system express the openings of their ducts are readily seen
vestibular reflexes in the absence of
when the margin of the lid is everted, and
appropriate stimuli. These individuals
commonly have resting nystagmus, a the glands themselves are usually visible
head tilt, and a tendency to lean, circle, as yellowish‐white columns under the
or fall to one side. mucous membrane on the inner surface
of the lid. The tarsal glands produce an
important oil layer of the tear film.
Vision The conjunctiva is the mucous mem­
brane that lines the inside of the palpebrae
The eye is an elaborate organ whose and part of the anterior surface of the
primary function is to collect and focus eyeball (excluding the clear cornea). Diseases
light upon the photosensitive retina. It of the conjunctiva are the most common
lies within a coneshaped cavity of the skull, eye disorders. The conjunctiva is rich in
the orbit, which houses the eyeball (globe) mucus‐producing glands, lymphocytes,
and a number of other soft tissue struc­ nerves, and blood vessels. The very small
tures, the ocular adnexa (e.g., muscles, space between the eyelids and the surface
glands), that act upon the eyeball in service of the eye is the conjunctival sac, and it is
of its light‐collecting function. Unlike the into this space that eye medications are
human orbit, which is a complete bony usually instilled.
cone, the ventral portion of the orbit of Inflammation of the conjunctiva, or
domestic species is bounded by soft tissues, conjunctivitis, is characterized by red-
notably the pterygoid muscles. ness and increased mucus production.
Cancer eye, squamous cell carcinoma of
the conjunctiva, is relatively common in
Ocular Adnexa Hereford, Holstein, and shorthorn
breeds of cattle.
Palpebrae. Two mobile folds of haired Domestic species possess a nictitating
skin protect the anterior aspect of the membrane, or third eyelid. This is a fold
eyeball. These are the eyelids, or of mucous membrane arising from the
palpebrae. The gap between the margins ventromedial aspect of the conjunctival
of the two palpebrae is the palpebral sac between the eyeball and palpebrae. It is
fissure, and its size is controlled by the given rigidity by a T‐shaped cartilage
muscles of the eyelids. A layer of dense within it, and it smooths the tear film and
connective tissue in the palpebrae, the protects the cornea.
tarsal plate (tarsus), affords them a The third eyelid has at its base a serous
certain amount of rigidity. The palpebrae gland, called simply the gland of the third
have thin but otherwise typical haired eyelid, which normally contributes about
skin on their superficial side. This skin 50% of the tear film. Ruminants, the pig,
ends at the lid margin with a sharp and laboratory rodents possess another
transition to mucous membrane. The deeper gland associated with the third
margin may have cilia (eyelashes). eyelid. This is the harderian gland. It, too,
Abundant modified sweat and sebaceous contributes to the tear film.
glands are associated with the lid margin.
A row of large modified sebaceous glands, Lacrimal Apparatus. The lacrimal
the tarsal glands (meibomian glands), apparatus comprises a series of serous,
is especially clinically significant, as they seromucoid, and mucous glands and the
commonly become infected, develop duct systems that drain their secretions
tumors, or become impacted. The tarsal from the conjunctival sac (Fig. 12‐11).
glands are present in both palpebrae and It provides a moist environment for the